The present disclosure relates to covers or tarping systems for open-topped containers, and more specifically to an actuation mechanism for pivoting the cover over a truck bed.
Some hauling vehicles, such as dump trucks, include open-topped containers used for hauling or storing various materials. For example, in a typical dump truck application, the dump body is used to haul a variety of particulate material, such as gravel, aggregate or similar products. In addition, some hauling vehicles carry organic materials, such as grain or produce.
Depending upon the nature of the materials stored in the open-topped container, it is often desirable to provide a cover for the container. Of course, rigid covers are well known that may be hinged from one end of the container body. These rigid covers have gradually given way in the industry to flexible tarping systems because the flexible tarpaulin can be easily stowed when a cover is not necessary, such as when the dump bed is being loaded. Moreover, the flexible tarp is much easier to deploy than a rigid cover.
One tarping system for use with dump trucks is the Easy Cover® Tarping System, of Aero Industries, Inc. The Easy Cover® Tarping System includes a U-shaped bail member that is pivotally mounted at its ends to the base of the container body. The horizontal section of the U-shaped bail is attached to the tarp, while the free ends of the vertical elements are pivotally mounted. As shown in FIG. 1, a vehicle V having an open-topped body B, such as a dump truck, includes a tarpaulin cover 14, which is shown in its deployed configuration spanning the length of the container. The tarp cover 14 is wound and unwound from a tarp roller assembly 16 at one end (typically the forward end) of the bed.
A U-shaped bail member 10 is connected to one end of the tarp cover 14 and is pivotally mounted to the truck body B by way of an actuation mechanism 12. This actuation mechanism can take a variety of forms including extension springs, compression spring, and coil torsion springs which apply a torque or moment to the arms of the U-shaped bail member 10. When the actuation mechanism is released, it automatically pivots the bar, thereby unfurling the tarp from the tarp roller assembly 16. A hand crank or powered motor 18 can be provided to rotate the tarp roller in the opposite direction to wind the tarp into the roller assembly when it is desired to open the container top.
One such actuation mechanism implemented in the Easy Cover® Tarping System incorporates a “double-coil” spring as more fully described in U.S. Pat. No. 6,318,790 to Henning (the '790 Patent), the disclosure of which is incorporated herein by reference. As shown in FIG. 4 of the '790 Patent the actuation mechanism includes one or more elastically deformable double-coil springs having two coil portions concentrically wound around each other and disposed in a common plane with an integral center anchor section between each of the coil portions. A free reaction end of each coil portion is connected to an arm of the bail member through a pair of reaction posts mounted on the arm. The center anchor section is held fixed relative to the bail arm and is generally fixed to the dump body by an pivot shaft mounted thereto, such as the pivot shaft shown in FIG. 5 of the '790 Patent. As shown in FIG. 6 of the '790 Patent, the deployment mechanism includes a housing that sandwiches the double coil springs between opposed housing halves that are secured to the leg of the bail member.
The actuation mechanism disclosed in the '790 Patent thus provides a great amount of torque in a small package that is capable of meeting vehicle width limitation regulations. With tarping systems of this type, the torque in the springs is greatest when the cover is open and the springs are rotated to their maximum angular position. On the other hand, when cover is extended or closed the spring torque is at a minimum as the springs are unwound. The reduced torque means that the springs are not exerting sufficient force to hold down the end of the closed tarp when the vehicle is subject to road vibration and bounce. Auxiliary mechanisms may be provided to hold the tarp end down in the open position. It is desirable to provide an increased spring torque at the unwound position of the spring, but doing so necessarily increases the spring torque at the fully wound open cover position. Greater torque in a fully wound spring increases the risk of failure of the spring. The actuation mechanisms of the type described in the '790 Patent have an improved torque range that helps address this problem. However, in some vehicle applications it is desirable for the actuation mechanism to be mounted near the top rail R of the body B. An actuation mechanism mounted at the top rail necessarily travels through a broader angle than a mechanism mounted at the bottom of the container. For instance, in a typical bottom-mounted installation the actuation mechanism travels through a maximum range of about 140°, while a top rail mounted mechanism travels through a range of 160-170°. There is a need for an actuation mechanism that can maintain an appropriate torque throughout the larger range of travel of the top rail mounted system.